The present invention relates in general to detecting misfires occurring during normal in-use vehicle operation of internal combustion engines, and more specifically to measuring power loss during each particular cylinder firing to identify the occurrence of misfires.
Most automobiles employ a catalytic converter to reduce the amount of pollutants in the engine exhaust. However, when a cylinder misfires so that no or incomplete combustion occurs, uncombusted fuel is introduced into the exhaust which burns in the hot catalytic converter. The heat from fuel burning in the catalytic converter destroys the catalyst. Thus, it becomes desirable to detect and count engine misfires and signal the operator of the vehicle upon occurrence of excessive misfires so that steps may be taken to protect the catalytic converter.
It is also desirable to detect misfires in order to allow adaptive control of the combustion engine in order to improve engine performance or to possibly eliminate the condition leading to misfire or remove fuel to the misfiring cylinder and thereby protecting the catalyst.
The identity of a misfiring cylinder and the frequency of misfires can be recorded for later use during diagnosis and repair of the vehicle.
Gas pressure from combustion in a properly firing cylinder accelerates the engine crankshaft during the power stroke of that particular cylinder. If a cylinder misfires instead of properly firing, then friction, compression occurring in other cylinders, and the presence of an external engine load combine to produce a net deceleration during the power stroke. The actual deceleration is normally small since engines are intentionally provided with a flywheel having large inertial mass to allow smooth operation in spite of the periodic power stroke pulsations and random fluctuations in power.
Decelerations are also caused by load and torque variations during vehicle operation. During other driving conditions, it may also be normal for no significant power to be produced by a particular cylinder firing, such as during a closed throttle deceleration. As a result of these difficulties, prior art attempts to detect misfires through crankshaft acceleration computed from crankshaft velocity measurements has met with limited success.
In Hanson et al, U.S. Pat. No. 3,972,230, it is shown that a misfire results in an abrupt reduction in instantaneous speed during the power period in which the misfire occurs. An engine is operated an idle speed and velocity measurements for about 200 consecutive power periods are collected. An average deceleration rate is found for each cylinder and individual deceleration rates are compared to the cylinder average deceleration rate to detect individual misfires. However, this method works only at idle speed and even then it requires averaging over many engine cycles in order to identify a misfiring cylinder because the technique has a poor signal-to-noise performance.
In Citron et al, U.S. Pat. No. 4,532,592, the change in instantaneous engine speed between successive cylinders provides a basis for determining the relative combustion efficiency of each cylinder. An index of performance is calculated based on crankshaft rotational time intervals which are digitally filtered. In order to get an accurate measure of the relative torque produced by a given cylinder, the index of performance is averaged over several successive firings. Furthermore, the method disclosed in this patent assumes that an engine is operating at steady-state so that the sum of individual performance indices over an integral number of engine cycles will tend to zero. Therefore, the method described in this patent is incapable of accurate misfire detection during nonsteady-state (i.e., transient) operation of an engine which constitutes the majority of normal driving conditions.
Accordingly, it is a principal object of the present invention to provide a method and apparatus for detecting misfires in an internal combustion engine.
It is a further object of this invention to detect misfires based on readily available engine operating data using sensors which are typically already present within an engine for other purposes.
It is another object of this invention to detect engine operating conditions which could cause damage to a catalytic converter.
It is still another object of this invention to prevent damage to a catalytic converter.
It is a further object of this invention to improve drivability of a vehicle by responding to the occurrence of misfires in order to reduce or eliminate further misfires.
It is yet another object of this invention to detect the occurrence of misfires over a full range of speed and load of an internal combustion engine, either during steady-state operation or transient operation.
It is a further object of this invention to detect misfires in real-time on board a moving vehicle, the misfire detection achieving extremely low error rates.